1. Field of the Invention
The present invention generally relates to a package and an electronic component that has a package structure hermetically sealing a chip, and more particularly, to a package and an electronic component that has a package structure suitable for improving electrical characteristics such as stop-band attenuation of a filter device such as a surface acoustic wave device.
2. Description of the Related Art
Conventionally, surface acoustic wave devices (hereinafter referred to simply as SAW devices) have been used as electronic components each having a package in which a chip is hermetically sealed. A conventional SAW device normally includes a SAW device chip having a SAW element formed on a piezoelectric substrate, and a package in which the SAW device chip is hermetically sealed.
Such SAW devices are widely used in filter devices and oscillators of television (TV) receivers, videotape recorders (VTRs), DVD (Digital Versatile Disk) recorders, and cellular phone devices. More specifically, SAW devices are widely used in various kinds of circuits that process radio signals in frequency bands of 45 MHz to 2 GHz. Such circuits include transmission band-pass filters, reception band-pass filters, local oscillation filters, antenna duplexers, intermediate frequency filters, and frequency modulators.
As those signal processing apparatuses have dramatically become smaller in size in recent years, there is an increasing demand for smaller electronic components such as SAW devices to be employed in those apparatuses. Especially, surface-mounted type SAW devices that are low in height are strongly required for portable electronic devices such as cellular phone devices.
So as to perform surface-mounting of a SAW device, a package structure made of ceramics is normally used. Such a package structure is disclosed in Japanese Unexamined Patent Publication No. 7-336186, for example. If the package size is large, however, a ceramic package is likely to be expensive.
Meanwhile, a less expensive package that is not made of ceramics has also been suggested, for example, in Japanese Unexamined Patent Publication No. 2001-60842. Such a package structure has a metal portion and an insulating portion. The insulating portion is formed in through holes in the metal portion, and leads for external connections are embedded in the insulating portion. A crystal oscillator to be housed in the package is supported at both ends, and is attached to the package in such a manner that oscillation is not hindered.
The package disclosed in Japanese Unexamined Patent Publication No. 2001-60842, however, is not suitable for housing a chip such as a SAW device chip that is to be wire-bonded and die-mounted onto a package, because a crystal vibrator is supported by the package at both ends.